Ricardo Uauy, MD, PhD; Magdalena Araya, MD, PhD
J Pediatr 145:3; 283-285 September 2004
Human milk oligosaccharides (HMOS) comprise the third largest solid component in mature human milk (12-14 g/L) after lactose and fat; there are more oligosaccharides than protein in breast milk. HMOS are resistant to digestion in the small intestine and are able to reach the colon intact. There they exert their effect directly by promoting the growth of specific microbial flora. They can be absorbed and excreted in the urine and may protect from urinary tract infections. Indirectly they may also act through their fermentation, modifying colonic pH, generating substances that may affect colonic cells, gut-associated immune cells, and other bacteria. In contrast, cow’s milk contains relatively minor amounts of oligosaccharides. The physiologic effects of oligosaccharides in the gut are related to their support of the growth of lactic acid-generating bacteria, a so-called ‘‘prebiotic’’ effect. This conditions an acid environment that prevents the growth of gram-negative and other potentially pathogenic bacteria. In addition, their secondary structure allows them to act as receptor analogues for cellsurface sites in the gut epithelium, preventing the adhesion of microbes to the gut mucosa.
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